The CERES project has now produced two decades of observed data on the Earth’s Energy Imbalance (EEI) and has revealed substantive trends in both the reflected short-wave and outgoing long-wave components. Available CMIP6 simulations suggest that these trends are incompatible with purely internal variability, but that the full magnitude of the trends are harder to match. There is however an apparent sensitivity to the representation of aerosols. Unfortunately, the CMIP6 protocol only uses observed forcings to 2014 (and SSP projections thereafter), and furthermore, many of the ‘observed’ drivers have been updated substantially since the CMIP6 inputs were defined. Most notably, the sea surface temperature (SST) inputs for AMIP-style atmospheric simulations have been revised and now show 50% greater trends since 1979. Additionally, estimates of short-lived aerosol and gas phase emissions have been substantially updated. These revisions will likely have material impacts on the EEI.

We therefore propose a new, relatively low cost, model intercomparison (CERESMIP) that would be focused on the CERES period, with updated forcings to the end of 2021. Model groups would be asked to submit atmosphere-only simulations, using updated SST, forcings and emissions from 1990-2021. The diagnostic focus will be on the EEI and atmospheric feedbacks, and so diagnostics should include output from the COSP simulator. The Tier 1 request would consist of a single AMIP simulation, while the Tier 2 request would focus on uncertainties in the applied forcings, atmospheric composition and single forcing response.

We will present some preliminary results and request participation from a wide group of models.